Pesticides in Imported Produce

Monitoring pesticide residues in fruit and vegetables remains a key priority for international food safety. Increasing imports from countries, such as China and India, with substantially different regulations to their Western counterparts, highlights the need for stringent pesticide monitoring. Tandem mass spectrometry coupled to chromatography systems, such as gas chromatography mass spectrometry (GC-MS) and liquid chromatography mass spectrometry (LC-MS), operating in multiple reaction monitoring (MRM) mode has emerged as the industry standard for monitoring residues in fruits and vegetables. However, a continuing challenge in multi-residue analysis is finding a sample preparation method that is as easy, fast, and cost-efficient as possible.

The U.S. FDA recommends the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method for residue screening based on MRM with advanced gas or liquid chromatography coupled mass spectrometry systems. However, these QC methodologies can be complex and time consuming, particularly for trace pesticide analysis in complex biological matrices. A modified QuEChERS preparation protocol developed by the FDA Irvine laboratory in California can extract multiple classes of pesticides from a wide variety of samples. This methodology presents an alternative to the conventional QuEChERS technique and allows the extracted matrix to be directly injected into the instrument, saving preparation time. This article demonstrates that the modified QuEChERS sample preparation protocol is a simple, less expensive, and unified alternative to conventional QuEChERS protocol.

Challenges of International Trade

The liberalization of global trade has greatly benefited emerging economies around the world. Following its accession to the World Trade Organization in 2001, China is now a major global producer of agricultural products, especially fruits, vegetables, rice, and pork. In 2009, China was the fourth leading global agricultural exporting country (behind the U.S., Brazil, and Canada), with exports to the U.S. alone reaching approximately $3.3 billion in 2010. However, the lack of global standardization or global consensus on the use of pesticides is a barrier that limits producers from accessing the full potential of the export market. Imports from regions where pesticide use is less restricted to those with stringent regulations are frequently subject to detention and often returned to their country of origin or disposed of, resulting in an immediate loss in investment.

The benefits for global standardization have now been recognized and governments around the world are beginning to take steps to bring the regulations guiding crop growth and maintenance in line with their Western counterparts. For instance, China has recently limited the use of harmful pesticides that are widely banned on international markets, while Pakistan has announced its intention to bring rice and mango production in line with FDA guidance. However, accurate and robust pesticide quantification methods are essential to determine whether consumable products comply with international and domestic regulatory standards.

Extracting multiple pesticide species from fruits and vegetables is a challenging process due to the complex biological matrices. Conventional analytical techniques have, until recently, been unable to deliver the sensitivity required to achieve reliable trace level analysis. Consistently achieving the high levels of sensitivity required can also be a time intensive and laborious task, which is undesirable for a high-throughput routine QC laboratory. Developing analytical technologies and screening methodologies to be able to quickly and accurately qualify and quantify trace pesticide residues is therefore a priority for both instrument developers and regulatory bodies.

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Figure 2a (left): MRM chromatograms for selected pesticides at 1 ppb in spinach extract by LC-MS/MS; Figure 2b (right): MRM chromatograms for selected pesticides at 5 ppb in spinach extract by GC-MS/MS.

Advancing Detection Procedures

The USDA QuEChERS method for pesticide residue analysis was presented at the 2002 European Pesticide Residue Workshop. QuEChERS simplifies the analysis of pesticide residues in food products, including fruits and vegetables, and takes advantage of advances in LC-MS and GC-MS. The method is now standardized within AOAC 2007.01 EN15662, having proven more productive than conventional preparation techniques.